Secondary batteries are used as replacements for primary batteries, and have been wide spread as power sources for electric appliances such as mobile phones and information technology (IT) devices. In particular, non-aqueous electrolyte secondary batteries represented by lithium ion batteries have high energy density and are increasingly applied to large industrial electric apparatuses such as electric vehicles.
A conventional non-aqueous electrolyte secondary battery has connection parts each of which is for connecting (i) a corresponding one of current collectors disposed inside the container of the battery and is electrically connected to a corresponding one of a positive electrode and a negative electrode in the electrode assembly disposed inside the container and (ii) a corresponding one of the electrode terminals outside the container, so that electric energy generated by the electrode assembly can be extracted. Each of the connection parts is formed integrally with the corresponding electrode terminal to penetrate through the cap part of the container, so as to connect the corresponding current collector inside the container and the electrode terminal outside the container. For this reason, the cap part has through-holes for allowing penetration of the respectively corresponding connection parts.
The container is generally made of metal, and thus there is a need to insulate the container areas in which through-holes are formed and the electrode terminals, the connection parts, and the current collectors. This is because a short circuit is caused in the container if the connection parts penetrate through the cap part of the container via the through-holes without any insulation. In addition, the container contains electrolyte together with the electrode assembly, and there is a need to prevent the electrolyte from leaking to the outside of the container through the through-holes.
In order to insulate the container and the electrode terminals, the connection parts, and the current collectors and prevent the electrolyte from leaking to the outside of the container through the through-holes, a conventional energy storage element includes insulation sealing members provided to cover the cap part areas in which the through-holes of the container are formed at the outside and inside of the cap part of the container. For example, both the insulation and sealing between the container and the electrode terminals, the connection parts, and the current collectors are achieved by means of the connection parts pressure-bonding the electrode terminals outside the container and the current collectors inside the container in a state where the container areas having the through-holes are covered at both the inside and outside of the cap part of the container by the insulation sealing members (see Patent Literature below).